aws-stepfunctions-tasks: EcsRunTask is not actually a construct?

### Describe the bug

`EcsRunTask` implements `IConstruct` even though to my understanding it's not actually a construct (that's my understanding from reading [design guidelines](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md) as well as [the user guide](https://docs.aws.amazon.com/cdk/v2/guide/constructs.html#constructs_lib)) as it does not represent a [CloudFormation resource definition](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/AWS_StepFunctions.html).

### Expected Behavior

`EcsRunTask` does not implement `IConstruct`.

### Current Behavior

`EcsRunTask` implements `IConstruct`.

### Reproduction Steps

Library API.

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### CDK CLI Version

N/A

### Framework Version

2.118.0

### Node.js Version

N/A

### OS

N/A

### Language

TypeScript

### Language Version

N/A

### Other information

_No response_

Start by locating the EcsRunTask definition in aws-stepfunctions-tasks and read the linked design guidelines and constructs documentation. Check references to its IConstruct type before deciding whether the public API should change; done means the implementation and affected API checks consistently reflect the intended construct behavior.

Written by the indexing model from the issue text.